Second Series.— Polarization by Reflection. 365 
Rays out of 100 polarized. 
Argand-lamp without reflector, é : é 55 
Dark heat, from brass about 700°, : : b 61 
Incandescent platinum, . : r a3 ; 65 
32. This result would be explicable on the supposition that 
the angle of incidence was that which corresponds to the pola- 
rizing angle for heat from incandescent platinum, whilst it was 
too small for the more refrangible heat from an Argand burner, 
and too great for the less refrangible heat wholly unaccompanied by 
light ; nor is this view devoid of plausibility, as will immediately 
be seen, though the troublesome nature of the experiments, and 
the smallness of the numerical results, prevented me from prose- 
cuting them farther in this way, than merely to verify generally 
the preceding results. 
33. These experiments were made, as usual, by disclosing 
the source of heat only for the time that the needle was making 
its first swing. Thus the effect of absorbed heat was to a great 
extent avoided. It was worth inquiring, however, whether the 
acquired heat of the first plate AB, Fig. 6, could by possibility 
produce an effect similar to that of polarization in rectangular 
positions. For this purpose I used the tin water-canister al- 
ready described (art. 19), which was subsituted for the plate AB. 
Whilst, however, it remained vertically below CD, as in F ig. 6, 
such a stream of hot air was carried upwards to the pile as to 
spoil the experiment. But when the plane of reflection at 
CD was made horizontal, as shewn in Fig. 8, the effect could 
be accurately observed, and the result was the same as in the 
case of transmission, namely, that even on this enormously exag- 
gerated scale of error, the quantities of heat reflected to the pile 
in parallel and rectangular positions of the surface were almost 
precisely the same. (Dec. 21. 1835.) 
34. A mica-plate placed between the two reflecting surfaces 
in Fig. 6, perpendicularly to the reflected ray, is capable of de- 
polarizing the heat, as in the case of heat polarized by transmis- 
